Substrate processing, e.g., semiconductor wafer fabrication, often requires that substrates be substantially free of defects. Defect detection systems are often employed as part of the manufacturing process to locate defects on a substrate. Certain types of defect detection systems may be calibrated using a deposition of polystyrene latex (PSL) spheres as a known source of scatter signal. Radiation is directed toward a calibration sample substrate having PSL spheres of a known size distribution deposited on its surface. The measured amplitude of radiation scattered by the PSL spheres may be used as a standard for matching the response of a defect detection system to a known source of scattering. The use of a deposition of polystyrene latex (PSL) spheres as a known source of scatter signal allows meaningful comparisons to be made between scatter signals from PSL spheres as measured by bright or dark field detection scanning surface inspection systems of different designs. The measured PSL scatter signal amplitude may be compared to scatter signals for a sample substrate having real surface defects whose identity and true size are unknown. This practice provides a basis for quantifying system performance as used in related standards concerned with parameters such as sensitivity, repeatability and capture rate.
As the size of semiconductor integrated circuit features decreases detection of smaller and smaller defects becomes more critical. As a result, shorter wavelength radiation may be used to detect smaller defects. Given this requirement a defect detection system may expose a PSL calibration target to radiation 257 nanometers or shorter wavelength radiation. Such radiation has been observed to degrade conventional polystyrene latex (PSL) spheres used to calibrate surface inspection systems. This can lead to additional cost and downtime associated with recoating or replacement of a PSL calibration target.
It is within this context that embodiments of the present invention arise.